The background description provided herein is for the purpose of generally presenting the context of the present invention. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.
The p-n junction diode and field-effect transistor (FET) are the two most ubiquitous building blocks of modern electronics and optoelectronics. In recent years, the emergence of reduced dimensionality materials has suggested that these components can be scaled down to atomic thicknesses [1, 2]. Although high performance field-effect devices have been achieved from monolayered materials [3, 4] and their heterostructures [5-10], a p-n heterojunction diode derived from ultrathin materials is notably absent and constrains the fabrication of complex electronic and optoelectronic circuits.
In bulk semiconductor p-n junctions, the doping level is primarily controlled via diffusion or implantation of substitutional impurities, which implies minimal control over the doping profile following device fabrication. In contrast, atomically thin semiconductors can be electrostatically doped by applying a bias to a capacitively coupled gate electrode. The atomically thin structure of these materials also enables doping modulation of the overlying layers in a vertically stacked heterostructure [6]. For example, this strategy allows gapless graphene to be used in field-effect tunneling devices in combination with other layered materials [6, 8]. Vertical 2D heterostructures have also been used to create high performance MOSFETs [5], tunneling FETs [6], barristors [15], inverters [7], and memory devices [9, 10] in addition to facilitating the study of novel physical phenomena in layered materials [16, 17]. Similarly, in-plane graphene heterostructures have served as the basis of unique 2D devices [18-20]. Although the nearly perfect 2D structure and low density of states in graphene provide advantages in some heterostructure devices, its gapless nature prevents the formation of a large potential barrier for charge separation and current rectification. In particular, the lack of monolayer semiconductors with complementary (p and n) polarities has precluded the realization of a gate-tunable heterojunction p-n diode.
Therefore, a heretofore unaddressed need exists in the art to address the aforementioned deficiencies and inadequacies.